Method for controlling a vehicle drive unit having a continuously variable transmission

Abstract

A method for controlling a vehicle drive unit, which comprises a drive engine and a transmission with a continuously variable gear ratio, comprises the following steps: a) the required vehicle acceleration (ASOLL) is calculated from a throttle control lever position (XFP, XHG) and the current speed of travel (VFZ), b) a required transmission variation (IGDSOLL 1 ) is calculated from the required vehicle acceleration (ASOLL) and the current rotation speed (NMOT) of the drive engine, c) a limited required transmission variation (IGDSOLL) is determined from the required transmission variation (IGDSOLL 1 ) such that the engine rotation speed (NMOT) does not fall below a value which depends on the position of the power control element (XEP) of the drive engine, d) the continuously variable transmission is varied in accordance with (IGDSOLL); e) the actuation parameter (XEPSOLL) for the power control element of the drive engine is obtained directly from the throttle control lever position (XFP, XHG).

What is claimed is:  
     
       1. A method for controlling a vehicle drive unit comprising a drive engine and a transmission having a continuously variable gear ratio, in the case of which method command signals and state signals are used to generate control signals for the drive engine and for the transmission, with a required gradient being determined for the transmission gear ratio, distinguished by the sequence of the following steps: 
       a) the required vehicle acceleration (ASOLL) and the output drive rotation speed gradient (NABDSOLL) are calculated from a throttle control lever position (XFP, XHG) and the current speed of travel (VFZ) by means of a family of characteristics (#ASOLLF, #ASOLLR),  
       b) a required transmission variation (IGDSOLL 1 ) is calculated from the required vehicle acceleration (ASOLL) and the current rotation speed (NMOT) of the drive engine,  
       c) a limited required transmission variation (IGDSOLL) is determined from the required transmission variation (IGDSOLL 1 ) such that the engine rotation speed (NMOT) does not fall below a value which is a function (NMOTMMAX) of the position of the power control element (XEP) of the drive engine,  
       d) the continuously variable transmission is varied in accordance with (IGDSOLL);  
       e) the actuation parameter (XEPSOLL) for the power control element of the drive engine is obtained directly from the throttle control lever position (XFP, XHG).  
     
     
       2. The method as claimed in claim  1 , wherein further families of characteristics (#ASOLLFKR, #ASOLLRKR) or calculation functions (#FNASOLLB, #FNASOLLTM) are used to calculate the required vehicle acceleration (ASOLL) on the basis of command signals (FLKR, FLTM). 
     
     
       3. The method as claimed in claim  2 , wherein, when the Tempomat function is switched on, the current speed of the vehicle (VFZ) is stored as a required value (VSOLLTMMEM) and, as a consequence of this, the required vehicle acceleration (ASOLLTM) and the output drive rotation speed gradient (NABDSOLLTM) are calculated as a function of the speed error (VSOLLTMMEM−VFZ), and the required transmission variation (IGDSOLL) is calculated from this, taking account of the current engine operating state. 
     
     
       4. The method as claimed in claim  1  (e), wherein the drive engine is a diesel engine having a control rod as the power control element, and wherein its actuation parameter is the required position (XEPSOLL, XEPSOLLFP) of the control rod. 
     
     
       5. The method as claimed in claim  1  for a vehicle drive unit which, in addition to the vehicle, also drives a power takeoff shaft, and with a throttle control pedal and a manual throttle control being provided as the throttle control lever, wherein, when the manual throttle control is activated, its position (XHG) determines only the actuation parameter (XEPSOLL) for the drive engine, and the position (XFP) of the throttle control pedal causes only a variation of the transmission gear ratio (IG). 
     
     
       6. The method as claimed in claim  1  (b), wherein the gradient of the rotation speed (NMOTD) of the drive engine is also taken into account in order to take account of the current rotation speed (NMOT) of the drive engine when determining the required transmission variation (IGDSOLL 1 ). 
     
     
       7. The method as claimed in claim  1 , wherein a stationary position control process is provided, which is carried out with the following steps: 
       a) when the throttle control lever is not being operated and the vehicle is stationary for the first time, the required stationary position of the vehicle (NABI) is defined by initialization of the value of the integral,  
       b) calculation of the error from the required stationary position of the vehicle (NABI) by integration of the output drive rotation speed (NAB),  
       c) a required output drive rotation speed gradient (NABDSOLL) is calculated from the error from the required stationary position of the vehicle (NABI), by means of a function (#FNNABDSOLL) and, possibly, also from the output drive rotation speed (NAB) and a further function (#FNNABDSOLL 1 ),  
       d) the stationary position control process is ended by operating the throttle control lever.  
     
     
       8. The method as claimed in claim  1 , wherein the required transmission variation (IGDSOLL) limiting is carried out in the following steps: 
       a) the engine rotation speed (NMOTMMAX) which corresponds to the desired engine operating point and which should not be undershot is calculated from the position of the power control element of the drive engine (XEP) by means of a function (#FNXEPNMOT),  
       b) a control error (DNMOT) is formed from the current engine rotation speed (NMOT) and the desired engine rotation speed (NMOTMMAX),  
       c) a required engine rotation speed gradient (NMOTDMIN; NMOTDMIN 1 ) is determined from the control error (DNMOT) using a predetermined function (#FNNMOTDMIN 1 ),  
       d) a gradient control error (DNMOTDMIN) is determined from the actual engine rotation speed gradient (DNMOT) and the required engine rotation speed gradient (NMOTDMIN; NMOTDMIN 1 ), and a limit value for the first derivative of the required transmission variation (IGDDSOLLLIM) is calculated from this using a function (#FNIGDDLIM), and is used for limiting,  
       e) the limit value (IGDSOLLLIM 1 ) is calculated from the required transmission variation (IGDDSOLLLIM) by integration, and (IGDSOLL 1 ) is then limited to a maximum value of (IGDSOLLLIM 1 ).  
     
     
       9. The method as claimed in claim  8 , wherein, in addition to step c) of claim  8 : 
       a) a minimum engine rotation speed (NMOTMIN) is determined as a predetermined function (#FNNMOTMIN) of the transmission gear ratio (IG) or of the vehicle speed VFZ,  
       b) a rotation speed error ((downward)) (NMOT−NMOTMIN) is formed from the current engine rotation speed (NMOT) and the minimum engine rotation speed (NMOTMIN),  
       c) an engine rotation speed gradient (NMOTDMIN 2 ) is formed from the control error (NMOT−NMOTMIN) using a further predetermined function (#FNNMOTDMIN 2 ),  
       d) the greater of the two engine rotation speed gradients (NMOTDMIN 1 , NMOTDMIN 2 ) is selected as the final engine rotation speed gradient.  
     
     
       10. The method in claim  1 , wherein the require transmission variation (IGDSOLL 1 ) is reduced as it approaches the range boundaries. 
     
     
       11. The method as in claim  1 , wherein the output drive rotation speed (NAB) is determined from rotation speeds of members of the summing epicyclic transmission.